One process in the production of coated conductors (superconductive tapes or films) has been referred to as a thick film process where the thickness of the superconductive layer is generally at least one micron in thickness. In the thick film process, it has been shown that YBCO thin films on single crystal substrates can achieve critical current density (Jc) values of over 106 amperes per square centimeter (A/cm2) at 77 K. For non-epitaxial or amorphous substrates, the use of a suitable buffer layer to provide the necessary structural template has been previously developed.
One method of producing the coated conductor has been to deposit a textured film of a suitable buffer material onto a random, polycrystalline metal substrate. To obtain the best results, the textured film is deposited upon the metal substrate by ion-beam-assisted deposition. The preferred material for deposition by IBAD is magnesium oxide (MgO). IBAD MgO is an attractive process for making a textured film on a polycrystalline substrate because it is relatively fast and, hence, commercially feasible to scale into an industrial production process. The use of MgO has replaced the use of yttria-stabilized zirconia (YSZ). YSZ was the first material to be successfully deposited via IBAD to obtain a good textured film on which high quality YBa2Cu3Oy (YBCO) was deposited with a high critical current density (Jc) and high critical current (Ic). The use of MgO rather than YSZ speeds up the process of forming a similar quality film by as much as 100 times. One reason that limited the move to the use of a MgO layer was difficulties with materials compatibility, i.e.; MgO tended to react with other materials in the various layers. For example, while IBAD YSZ layers were largely unreactive with the subsequently deposited superconducting films, MgO films have been found to react with a YBCO layer.
Thus, further improvements in the coated conductors have been desired. After extensive and careful investigation, improvements have been found to the preparation of superconducting films on polycrystalline substrates such as flexible polycrystalline metal substrates with an IBAD MgO layer.